Exercise dumbbells are well known in the art and prevalent in the exercise equipment industry. Generally speaking, each dumbbell includes a handle and a desired number of weights or plates which are typically secured to opposite ends of the handle. The dumbbell is lifted up subject to gravitational force acting on the mass of the handle and any attached weights.
Some prior art dumbbells are made as fixed weights, and some people seem to prefer fixed weight dumbbells, perhaps because they are simple to use and solid in construction. However, a disadvantage of fixed weight dumbbells is that numerous such dumbbells are required to provide a range of weight resistance.
Other prior art dumbbells include handles and weight plates that the user is able to add to and/or remove from the handles. These variable weight dumbbells provide an economy of scale because only a few weights may be combined in a variety of ways to provide a range of weight resistance. On the other hand, these variable weight dumbbells require time to change between levels of weight resistance (particularly since a change is typically made to each end of two separate handles), and the loose weight plates may present a storage problem, as well.
Still other prior art, adjustable weight dumbbells (and barbells) do not require the user to handle the weight plates during changeovers, and they maintain the weight plates in orderly fashion when not in use. Examples of these more sophisticated, “selectorized” free weight assemblies are disclosed in U.S. Pat. No. 4,284,463 to Shields (discloses a dumbbell assembly having opposite side weights which are maintained in alignment on a base and selectively connected to a handle by means of cam driven pins on the weights); U.S. Pat. No. 4,529,198 to Hettick, Jr. (discloses a barbell assembly having opposite side weights which are maintained in alignment on respective storage members and selectively connected to a handle by means of axially movable springs); U.S. Pat. No. 4,822,034 to Shields (discloses both barbell and dumbbell assemblies having opposite side weights which are maintained in alignment on a shelf and selectively connected to a handle by means of latches on the weights); U.S. Pat. No. 5,769,762 to Towley, III et al. (discloses various weight assemblies having a plurality of interconnected opposite side weights which are stored in nested relationship to one another and selectively connected to a handle by various means); U.S. Pat. No. 5,839,997 to Roth et al. (discloses a dumbbell assembly having opposite side weights which are maintained in alignment on a base and selectively connected to a handle by means of eccentric cams on a rotating selector rod; U.S. Pat. No. 6,033,350 to Krull (discloses dumbbell assemblies and other weight lifting members having opposite end weights that are maintained in alignment on a base and selectively engaged by means of selector rods that move in opposite directions to engage weights at respective ends of the weight lifting member); U.S. Pat. No. 6,322,481 to Krull (discloses a dumbbell assembly having opposite end weights that are maintained in alignment on a base and selectively connected to a handle by means of a selector rod that engages different combinations of the weights as a function of its position relative thereto). U.S. Pat. No. 6,540,650 to Krull (discloses mechanisms for preventing weight adjustments except when the dumbbell or other weight lifting member occupies a rest position relative to an underlying base).